Transparent Conducting Oxides on Polymer Substrates by Pulsed Laser Deposition
Promotion date: 8 March 2007
I worked with transparent conducting oxides. There are not many materials that are transparent and have conducting properties at the same time. Glass for instance is totally non-conducting, a metal has good conducting properties but is not at all transparent. There are some materials with both properties, the transparent semiconductors.
Transparent conducting oxides have both properties. Why is that so important?
Thin films of transparent semiconductors are widely used as transparent electrodes in applications such as solar cells, LED lights, LCD screens etcetera. But they need to be processed at high temperatures. Because of this they cannot be used on plastics: a major disadvantage because there are numerous applications thinkable.
So your research dealt with nanofabrication?
Partly. We studied the existing materials and the application of those on plastics, but we also researched the application of materials that haven’t been used before.
Let’s talk about the existing materials first.
A material that is often used for applications is Indium Tin Oxide. We used pulsed laser deposition technology to apply Indium Tin Oxide layers. We found that by using this technique there is no need to heat the substrate to manufacture high performance thin films, e.g. you can use a plastic substrate.
And industry is very happy?
Well, you still have to scale up the process. But it is possible to use this technology in an industrial environment, yes.
And what about the new material?
The new material is Zinc Iridium Oxide (ZnIr2O4). This is a P-type material (a semiconductor material in which the dopants create holes as the majority charge carrier). The principle of a LED light is based on the combination of P-type materials with N-type materials (a semiconductor material, with electrons as the majority charge carriers). The P N junctions (diodes) are the building blocks of electronics.
Existing transparent P-type conductors are not easy to fabricate, there aren’t that many and they cannot be made at low temperatures. We developed this new transparent material which proved to be P-type and can be fabricated at room temperature.
So you added a new material to the existing range?
Yes, you could say that. And the most important thing is that we added a new material to the small range of P-types. We found it towards the end of my PhD.
Does that mean that you were saved by the bell?
No, not at all. Halfway my PhD we had many interesting results with the N-type materials. (Published in Applied Physics Letters). But the keyword in my research was still the polymer (plastic) substrate. We then decided to look at possibilities for P-type transparent conductors that could be applied to plastic in which we succeeded. (Also published in Applied Physics Letters). The demonstration of a working P-N device can be seen as a bonus.
What did you enjoy most about doing a PhD?
The independence with which you can conduct your research. Of course you are working together, you talk together and the experience of colleagues is invaluable, but it is you who determines the direction. You are boss of your own time.
What are you going to do next?
Working as a post-doc at the UT and set up a business. With others we are looking into the viability of a company called SolMateS (Solutions in Material Sience). We found that industry has many questions in the field of material science and we would like to assist them in the innovation process.